Nonoscillating high frequency amplifier



NONOSCILLATING HIGH FREQUENCY AMPLIFIER Filed Oct. 5, 1929 INVENTOR; mas POSTHUMU5 BY WtLLEM DANIEL Van GOGH Patented Oct. 9, 1934 UNITED STATES NONOSCILLATING HIGH FREQUENCY I I AMPLIFIER Klaas Pcsthumus and Willem Daniel van Gogh, Eindhoven, Netherlands, assig'nors to Radio Corporation of America, a corporation of Dela- Ware Application October 3, 1929, Serial No. 396,961 In the Netherlands October 29, 1928 2 Claims. (Cl. 250-27) Our present invention relates to receiving circuits, and, more particularly, to high-frequency amplifiers free from self-oscillation.

When using, for example, a receiver comprising one or more stages of high frequency amplifiers, a detector and one or more low-frequency amplifiers, and, particularly, when receivin short waves, the drawback is encountered that the high frequency stages react on each other and on the detector. This is due to the fact that when one of the twofilament leads is connected to the anode current source, the other one has still a given alternating current potential relatively to the first mentioned lead owing to the l impedance of the filaments. It is because of this lead that oscillations of a high frequency amplifier are passed on to following high frequency stages, if any, and the detector.

In receiving circuit-arrangements which include in the anode circuit of a detector valve bypass condensers for conducting back the high frequency oscillations to the cathode, it is already known to use two condensers of like size which are connected respectively toeither of the poles of the filament and on the other hand to the anode.

In the case of discharge tubes having an indirectly heated cathode, which cathode is connected to the centre of a potentiometer connected in i parallel to the filament, it has been found, particularly when more than one high frequency amplifier is used, that the coupling above referred to may occur.

Accordingly, it is one of the main objects of the present invention to provide a radio installation, and, more particularly, a radio receiving circuit comprising two or more discharge tubes, the filaments of which are supplied from a common source of current, free from undue coupling by the use of a simple and novel means.

Another important object of the invention consists in connecting in parallel, or in series, or both in parallel and in series, with the filament leads between two or more of the valves in which high frequency currents occur, reactances of such size that any coupling between these valves along the said leads is avoided.

Another object of the invention consists in providing an amplifier comprising a plurality of discharge tubes having an indirectly heated cathode, each of said cathodes being connected to the centre of a potentiometer connected across the filament, in which a condenser is mounted between the centre of the said potentiometer and one or both of the filament leads.

The novel features which we believe to be characteristic of our invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically several circuit organizations whereby our invention may be carried into effect.

The invention will be more clearly understood by reference to the accompanying drawing in which two embodiments thereof are illustrated.

Fig. 1 shows part of the diagram of a receiving set having two high frequency amplifiers, a detector and a low frequency amplifier.

Fig. 2 shows diagrammatically the present invention embodied in a discharge tube having an indirectly heated cathode.

Referring to Fig. 1, the part of the diagram of a receiving set which is associated with the supply of the filaments of the discharge tubes is shown. The filaments 3, 4, 5 and 6 respectively of two high frequency amplifiers, a detector and a low frequency, amplifier are supplied from a storage battery (not shown) or similar source of current.

The lead 1 is connected to an anode battery 9. Since the high frequency currents in the anode circuits of the high frequency amplifiers and the detector will make their way through the cathodes of the said valves, and only the filament lead 1 is connected to the anode battery, the filament lead 2, owing to the impedance of the filaments which are connected in parallel, will be at a given alternating current potential relatively to the first mentioned lead. By bridging by a condenser '7 the filament leads between the tapping points of the filaments 3 and 4, the alternating current potential across the lead 2 will be neutralized, 95 and thus a mutual coupling of the two high frequency amplifying valves will be avoided.

It is of course highly inconvenient that the high frequency oscillations which might be generated in the lead 2 are capable of propagating towards the detector and the low frequency amplifier. In accordance with the invention this inconvenience may be entirely obviated by connecting a high frequency choking coil 8, of low ohmic resistance, in the part of the filament lead 2 between the tapping points of the cathodes 4 and 5.

Fig. 2 shows a feeding diagram of a discharge tube having an indirectly heated cathode 11. The filament 10, enclosed within the said cathode, is fed through the above mentioned leads 1 and 2.

tional heating current, a plurality of filaments likewise have connected between them a condenser 14 so as to ensure entire symmetry.

While we have indicated and described several systems for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of our invention as set forth in the appended claims.

.What we claimis: 1. In combination with a source of uni-direcof high frequency amplifiers connected in parallel, a filament of a detector in parallel with the said filaments, at least one condenser connected in parallel between two of the high frequency amplifier filaments to prevent high frequency coupling between the said two amplifiers, and a high frequency choke connected in series between the said detector filament and the next preceding amplifier filament.

2. In combination with a source of heating current having positive and negative terminals, a

detector and an audio frequency amplifier having heated elements connected in parallel across said terminals, a radio frequency choke coil having a low ohmic'resistance and the heated element of a radio frequency amplifier connected in series across the terminals of the detector heated element, one end of said choke coil being directly connected to the positive terminal of said detector heated element, a source of anode potential and a lead connecting the negative terminal of said last named source to the negative terminal of the heated element of said radio frequency amplifier.

KLAAS POSTHUMU S.

WILLEM DANIEL VAN GOGH. 

